In U.S. Pat. No. 3,691,140 to Silver, there are disclosed inherently tacky acrylate copolymer microspheres comprising a major portion of at least one alkyl acrylate ester and a minor portion of an ionic comonomer. As discussed in this patent, the microspheres can be prepared utilizing suspension polymerization techniques, which, prior to Silver, were considered unsuitable for the preparation of tacky polymers. In the technique described by Silver, the microspheres are prepared utilizing an emulsifier in a concentration greater than the critical micelle concentration without the necessity of externally added protective colloids or the like. The Silver microspheres are taught to be copolymeric in nature, requiring an ionic comonomer as an essential component thereof.
In U.S. Pat. No. 4,166,152 to Baker et al., it is disclosed that inherently tacky microspheres having physical properties similar to those disclosed in the Silver patent, i.e., inherent tack, infusibility, solvent dispersibility and solvent insolubility, can be prepared based not only on copolymers, but also on homopolymers, and which do not require the containment of an ionic comonomer. The microspheres are again taught to be prepared by aqueous suspension polymerization, and have a suspension stabilizer and an emulsifier as essential ingredients in their preparation.
In contradistinction to the foregoing patents, I have now discovered a process for the preparation of microspheres having physical properties similar to those of the prior patents, but which do not require the containment of an ionic comonomer therein, and do not require a suspension stabilizer in their preparation. These microspheres may be homopolymers or copolymers, are formed from alkyl acrylate or methacrylate monomers, and may also include a minor portion of a nonionic, vinylic comonomer.